EDINBURGH, Scotland -- A ring supposedly used as a secret sign by supporters of Bonnie Prince Charlie is on the auction block in Scotland.

Prince Charles Edward Stuart, King Charles III of England and Scotland to his supporters, led an unsuccessful uprising against King George II in 1745 while his father was still alive. While many in Scotland remained loyal to the House of Stuart, anyone who declared their support openly faced execution.

Colin Fraser, an auctioneer with the firm Lyon and Turnbull, told The Scotsman that rings were used to identify messengers from the prince in exile in France.

"This ring was used as a 'signature' when traveling with correspondence from Charles," Fraser said. "No document could carry a signature or seal, as if the bearer was found in possession of such marked papers by government troops, he would almost certainly have been sentenced to death."

Fraser said that the rings are described in histories and documents, but the one to be sold Wednesday is the only one known to still exist. It has an inscription, "CRIII1766: Charles Rex, 1766," dating it from after the death of his father, Prince James, in 1766.